Apparatus for measuring periodic biosignals emitted by an individual associated with a vehicle safety device - Patents.com

Abstract

The present invention relates to a device for measuring at least one periodic vital sign from an individual, intended to be attached to a safety device of a vehicle so as to be placed between said device and said individual, comprising: a vibration sensor, * a stack including an active layer extending parallel to a main plane and made of a piezoelectric material and two contact electrodes arranged on at least one face of the active layer; * a flexible support layer extending parallel to the main plane and including a printed circuit with two electrical terminals, the support layer being intended to be placed on an individual; * The present invention relates to a vibration sensor comprising: an electrical connection layer arranged between the laminate and the support layer for connecting each contact electrode to an electrical terminal; and an acoustic damping member intended to be arranged between a safety device and the vibration sensor, the acoustic damping member being integral with the support layer and arranged above the laminate and spaced apart from the laminate.

Description

[Technical field]

[0001] The present invention relates to the field of collecting periodic biosignals emitted by the human body, in particular the heart rate or the respiratory rate. The present invention relates in particular to a device equipped with a vibration sensor, associated with a safety device of a vehicle (for example a seat belt) and enabling the measurement of the user's heart rate. [Background technology]

[0002] Road accidents are a major problem in developed countries. The main causes of accidents include fatigue and falling asleep while driving. Within the European Union (EU), it is estimated that the latter is responsible for 20%-35% of serious accidents, resulting in nearly 6,000 deaths per year. In the EU, it is believed that integrating on-board fatigue detectors into vehicles could save 4,000 lives and prevent tens of thousands of injuries each year.

[0003] In parallel, research and development focusing on autonomous vehicles is accelerating. Indeed, if autonomous driving is far from being operational for market launch, everything seems to indicate that the first stages of "partially autonomous driving" under the driver's responsibility will become commonplace within the next few years. In this context, it is necessary to ensure that the driver has all of his / her vigilance and reaction capabilities if he / she has to resume control in an emergency situation. In this regard, several public and private organizations, including automobile and equipment manufacturers, are currently trying to find a viable solution for automatic fatigue detection in vehicles.

[0004] Some envisaged solutions, such as connected watches, bracelets or clothing belts, are too invasive for the user and ensure monitoring of the driver's physiological variables only if the driver thinks about wearing them and / or connecting them.

[0005] Other solutions propose integrating a module for measuring the heart rate with the vehicle's seat belt into the driver's torso. For example, document CN106725395 proposes a module for measuring the heart rate, comprising two metal electrodes that clamp the polyester strap of the seat belt. The heartbeat contracts an insulating material placed between the two metal electrodes, causing the distance between the two metal electrodes to change, thus modifying the capacitance value and providing information about the driver's heart rate. Summary of the Invention [Problem to be solved by the invention]

[0006] The invention also relates to solutions related to vehicle safety equipment, in particular to a small and sensitive device with a vibration sensor capable of capturing and analyzing periodic biosignals of individuals in a vehicle. [Means for solving the problem]

[0007] The present invention relates to a device for measuring at least one periodic biosignal from an individual, the device being intended to be mounted on a safety device of a vehicle and placed between the individual and the device, the device comprising a vibration sensor, the vibration sensor comprising: a stack including an active layer extending parallel to its main plane and made of piezoelectric material and two contact electrodes arranged on at least one face of the active layer; a flexible support layer configured to transmit deformations to the active layer of the stack with each pulse of a biosignal, the support layer extending parallel to its main plane, including a printed circuit with two electrical terminals, the support layer being intended to be placed on an individual; an electrical connection layer arranged between the laminate and the support layer, connecting each contact electrode to an electrical terminal; A vibration sensor comprising: The device further comprises an acoustic damping member intended to be placed between the safety device and the vibration sensor, said member being firmly connected to the support layer and positioned above and spaced apart from the stack.

[0008] According to other advantageous, non-limiting characteristics of the present invention, taken alone or according to any technically feasible combination, the following: the acoustic damping element is made of a flexible material having a hardness of 10 Shore OO to 80 Shore OO and comprises a cover rigidly connected by its periphery to the support layer; the cover is heterogeneous and comprises a second rigid material selected from a metal or a polymer having a hardness of 10 Shore D to 80 Shore D; the device comprises a mechanical damping element integrated wholly or partially on or in the acoustic damping element, the mechanical damping element being intended to be in direct or indirect contact with the safety device; the mechanical damping member comprises at least one damper and optionally a body forming a mass; the active layer of the stack has a thickness of less than or equal to 20 microns and a Young's modulus of more than or equal to 60 GPa; the device comprises an impedance matching layer (40) having an acoustic impedance comprised between 5.105 Pa·s / m and 3.106 Pa·s / m and arranged on a side of the support layer opposite to the side in contact with the electrical connection layer, the piezoelectric material of the active layer is chosen from ceramics in monocrystalline, polycrystalline or composite form; the contact electrodes have a cumulative thickness less than twice the thickness of the active layer; the support layer is self-supporting and has a thickness of less than or equal to 500 microns; the impedance matching layer has a thickness of 10 microns or greater; the electrical connection layer is formed by an interposer or an anisotropic conductive film, the support layer comprises a film disposed on a side of the printed circuit opposite to the side in contact with the electrical connection layer; the laminate and the support layer each have a first surface area and a second surface area on a major plane, the first surface area being no more than 30% of the second surface area; the support layer comprises a reinforcing structure rigidly connected to a peripheral zone of said support layer, and the sound-damping member is rigidly connected to the reinforcing structure, the printed circuit comprises wire connection elements for connecting the vibration sensor to an electronic terminal, The vibration sensor includes a peripheral seal; the device further comprises an electronic terminal connected to the vibration sensor for analyzing and interpreting the raw signal and for extracting the periodic biosignal or an output parameter representative of said periodic biosignal, the electronic terminal comprises an analog stage for conditioning the raw signal measured by the vibration sensor, an analog-to-digital conversion stage for the signal coming from the conditioning stage, and a digital signal processing stage for forming a digital signal and for calculating output parameters representative of said biosignal, The electronic terminal comprises a communication stage with an external system.

[0009] The present invention also relates to a safety system for a vehicle, a safety device associated with the seat and rigidly connected to the chassis of the vehicle at at least one direct or indirect contact point; - a device for measuring at least one periodic vital sign of an individual, as described above, attached to the safety device by means of a slide fastener; at least one mechanical energy absorber arranged at at least one contact point so as to isolate the safety device from mechanical vibrations of the chassis.

[0010] The safety device may be directly connected to the chassis by at least three contact points, a mechanical energy absorber being integrated into at least one of the contact points. The safety device can be connected to the seat, the seat being rigidly connected to the chassis by at least one contact point, and a mechanical energy absorber being integrated into said contact point. [Brief description of the drawings]

[0011] Other features and advantages of the present invention will become apparent from the following detailed description of the invention which refers to the accompanying drawings. [Figure 1] 1 shows a safety system comprising a device for measuring at least one periodic vital sign of an individual in a vehicle according to the invention. [Figure 2a] All or part of an apparatus according to the invention is shown in a schematic cross-sectional view. [Figure 2b] 1 shows all or part of a device according to the invention in a perspective cross-sectional view; [Figure 3a] All or part of an apparatus according to the invention is shown in a schematic cross-sectional view. [Figure 3b] 1 shows all or part of a device according to the invention in a perspective cross-sectional view; [Figure 4] 1 shows in plan view different shapes of the vibration sensor of a device according to the invention; [Diagram 5] 1 shows various configurations of a device for measuring periodic biosignals according to the present invention; [Figure 6a] Two examples of acoustic damping members (i) and (ii) and two examples of mechanical damping members (iii) and (iv) for a device according to the invention are shown. [Figure 6b] 1 shows a device according to the invention in association with a vehicle safety device. [Figure 7a] 1 shows a spectrogram A measured by a vibration sensor (alone) included in a device according to the invention, and a spectrogram B measured by a device according to the invention. [Figure 7b] 1 shows a spectrogram B, a spectrogram B' extracted from spectrogram B, a spectrogram B'' after applying a frequency filter, and a biological signal B'''' as a waveform, all captured and processed by an apparatus according to the present invention.

[0012] The same reference numbers in the figures may be used for the same type of elements. Some figures include schematic diagrams that are not to scale for ease of reading. In particular, layer thicknesses along the z-axis are not to scale with respect to lateral dimensions along the x- and y-axes, and the relative thicknesses of layers therebetween are not necessarily taken into account. The different possibilities (variants and embodiments depicted and / or detailed in the following description) must be understood as not being mutually exclusive and may be combined together. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The invention relates to a device 200 for measuring at least one periodic, regular or irregular biosignal of an individual. The periodic biosignal may in particular be the heart rate or the respiratory rate. The device 200 is intended to be attached to a safety device 1 in a vehicle (FIG. 1) so that the device 200 is placed between the individual and the device 1. The term "safety device 1" is understood to mean any device intended to secure a user to a seat in the vehicle, in particular a seat belt, one or more safety bars, a safety harness, etc. The vehicle may also be understood broadly and includes any means of transportation for a person, such as rolling, flying, gliding or floating.

[0014] The device 200 is preferably attached to the safety device 1 by means of a slide fastener, i.e. a fastener that can be clipped to the device 1 to fix the device 200 in a given position and that can slide (when not clipped) to allow each user to adjust the position of the device 200 on his chest according to his size and his obesity. Optionally, the fastener system may allow a free range of movement around the operating position for the user's comfort.

[0015] The apparatus 200 comprises a vibration sensor 100 and an acoustic damping member 110 . Various configurations of a vibration sensor 100 according to the present invention are shown in Figures 2a, 2b, 3a and 3b and will now be described. The vibration sensor 100 comprises a stack 10 extending parallel to a main plane (x, y), i.e. the main faces of this stack 10 are substantially parallel to said main plane (x, y) and the thickness of the stack 10 is measured along an axis z perpendicular to said main plane. In the present invention, the term "layer" means that the thickness of a layer (or stack) is generally significantly smaller than the lateral dimensions (in the main plane) of the layer.

[0016] The laminate 10 comprises an active layer 11, which consists of a piezoelectric material, preferably chosen from piezoelectric ceramics in monocrystalline, polycrystalline or composite form (matrix, generally corresponding to a dispersion of piezoelectric ceramic powder in a polymer). By way of example, the following ceramics may be mentioned: lithium niobate (LiNbOs), lithium tantalate (LiTaOs), potassium niobate (KNbOs), (BaTiOs), quartz (SiO2), lead magnesium niobate-lead titanate (PMN-PT), lead zirconate titanate (PZT), materials based on potassium sodium niobium lithium antimony (KNN-LS) or modified with calcium titanate (KNN-LS-CT), materials based on potassium sodium lithium niobium tantalum antimony (KNNLNTS), bismuth sodium titanate (BNKLBT), etc. In a manner known per se, the active layer 11 made of piezoelectric material will become polarized (thus generating a flow of charges resulting in a measurable electrical signal) when subjected to a deformation, in particular a deformation caused here by the angular frequency of a periodic biological signal.

[0017] The active layer 11 advantageously has a thickness of 20 microns or less and a Young's modulus of 60 GPa or more. These physical properties give the active layer 11 a high level of sensitivity (related to the small thickness of the active layer 11 and the fact that for a given deformation, the measured voltage is larger if the Young's modulus is higher) and provide the sensor 100 with a high signal-to-noise ratio to detect sound waves at frequencies related to periodic biosignals of the subject. The small thickness of the active layer 11 also facilitates miniaturization of the sensor 100. To further improve the sensitivity of detection of acoustic waves, the thickness of the active layer 11 can be 10 microns or less, or even 5 microns or less, ensuring that the thickness of the active layer 11 is sufficient to generate a bias voltage during deformation, typically greater than 500 microvolts. The lateral dimensions of the active layer 11 (in the main plane (x,y)) may for example be chosen to be between 500 microns and 50 mm, with small dimensions being naturally preferred for reasons of miniaturization of the vibration sensor 100.

[0018] The stack 10 also includes two contact electrodes 12, 13 arranged on one or both faces of the active layer 11 (i.e., on either side of the active layer 11), allowing the free circulation of charges driven by the polarization of said layer 11 (representing a periodic biological signal). Preferably, the contact electrodes 12, 13 have a cumulative thickness that is less than twice the thickness of the active layer 11, or less than the thickness of the active layer 11, and therefore each electrode 12, 13 advantageously has a thickness of less than 10 microns, or less than 5 microns. The contact electrodes 12, 13 may be made of a pure metallic material (e.g., Ag, Au, Pd, Pt, Cu, Ni, W, or Ti), a conductive alloy, or a two-dimensional (2D) conductive material (e.g., graphene). Between the conductive material of each electrode 12, 13 and the active layer 11, a diffusion barrier (e.g., made of TiN, WN, or TaN) and an adhesion layer (e.g., made of Cr or Ti) may be provided.

[0019] Advantageously, the stack 10 consists only of an active layer 11 and two contact electrodes 12,13.

[0020] The vibration sensor 100 also comprises a flexible support layer 30 extending parallel to the main plane (x, y) and including a printed circuit 31 with two electrical terminals 32, 33. An electrical connection layer 20 (which also forms part of the vibration sensor 100) is disposed between the laminate 10 and the support layer 30 and connects each contact electrode 12, 13 to the electrical terminals 32, 33.

[0021] The electrical connection layer 20 is formed by an interposer or an anisotropic conductive film (ACF). In all cases, the aim is that the two contact electrodes 12, 13 of the stack 10 can be reached on one and the same face of the stack 10, which face (called the lower face) is then associated with the connection layer 20. When the contact electrodes 12, 13 are respectively arranged on the lower face and on the other face (called the upper face) of the active layer 11, it is advantageous to provide a conductive via 14 that passes through said active layer 11 and electrically connects the electrode 12 arranged on the upper face to a stud 12a arranged on the lower face and electrically insulated from the other electrode 13 also arranged on the lower face. The interposer may be constructed from a thermoplastic (insulating) resin and a conductive material (eg nickel) that allows connection between each contact electrode 12,13 and the electrical terminals 32,33. Anisotropic conductive films are traditionally composed of conductive beads dispersed in an insulating polymer matrix, and when pressure or thermocompression is applied to the laminate 10 / ACF 20 / support layer 30, vertical electrical conduction is established between the electrodes 12a, 13 and the terminals 32, 33 through the conductive beads (usually with excess thickness), while the interlayer zones remain insulating. There are also Anisotropic Conductive Adhesives (ACA) that can be used to form the electrical connection layer 20. These adhesives are based on the same principle as the Anisotropic Conductive Films (ACF) described above, except that the polymer matrix is ​​replaced by a liquid precursor that can be thermally activated (by polymerization) to form the final polymer, and the end result remains similar to the ACF (conductive beads dispersed in an insulating matrix), but considering the fact that the application is done in the liquid phase, it is possible to significantly reduce the thickness of the electrical connection layer 20. It may also be envisaged to implement a more basic solution, namely a conductive paste for connecting each electrode and stud on the underside to the associated terminal 32, 33, and an insulating filler material for electrically insulating the electrodes 12a, 13 from each other and the terminals 32, 33 from each other. The electrical connection layer 20 is in contact with only one of the main faces of the laminate 10 ; the edges and the other main face of the laminate 10 are completely free without mechanical contact with the connection layer 20 . Thus, the electrical connection layer 20 is at least partially constructed from a conductive material and provides a direct vertical connection between the electrodes and the terminals, as opposed to a connection by a cable or wire, for example, optionally covered with insulation. The absence of a cable improves the sensitivity of the vibration sensor 100 and avoids the introduction of additional stiffness associated with the associated cables and welds into the structure. Thus, preferably, the electrical connection layer 20 is in direct and uniform contact with the entire main surface of the laminate 10. On the other side, the layer 20 is advantageously in direct and uniform contact with the surface of the support layer 30. The electrical connection layer 20 typically has a thickness of less than 50 microns, and more particularly, a thickness of between 1 micron and 10 microns.

[0022] The support layer 30 is advantageously a self-supporting layer having a thickness of less than 500 microns, which gives it the necessary flexibility. According to one variant, the support layer 30 consists essentially of the material forming the printed circuit 31 (for example a composite of epoxy resin reinforced with glass fibres). According to another variant, the support layer 30 also comprises a membrane 35, the printed circuit 31 then being located between the membrane 35 and the electrical connection layer 20 (Figures 2a and 3a). The material of the membrane 35 and its thickness can therefore be selected and adjusted to give the support layer 30 a targeted flexibility. The membrane 35 may for example be made of metal, polyvinyl chloride (PVC) or epoxy and glass fibre. By way of example, the membrane 35 (if present) may have a thickness of 50 to 300 microns and the printed circuit 31 may have a thickness of 30 to 200 microns. Typically, the support layer 30 has a stiffness of 1,150,000 N / m to 6,900,000 N / m. The flexibility of the support layer 30, in conjunction with its thickness and its stiffness, allows it to effectively transmit deformations to the active layer 11 with each pulse of the biosignal.

[0023] Advantageously, the laminate 10 and the support layer 30 have a first surface area and a second surface area, respectively, in the main plane (x, y), the first surface area being equal to or less than 30% of the second surface area. The laminate 10 can be arranged in the central part of the support layer 30, particularly for ease of assembly, or on the periphery so as to interfere as little as possible with the deformations of said support layer 30, which are caused by the periodic pulsation of the biosignal to be measured, but the overall objective is to optimize the deformations undergone by the laminate 10 depending on the geometry of the vibration sensor 100. It should be noted that, although shown in the form of a square, the laminate 10 of the vibration sensor 100 can of course have any shape.

[0024] According to a first embodiment of the vibration sensor 100, the support layer 30 is intended to be in contact with an individual. The support layer 30 then deforms due to the periodic pulsing of the biosignal and transmits this deformation to the active layer 11 of the stack 10.

[0025] According to the second embodiment, the vibration sensor 100 is ideally 5.10 5 Pa·s / m~3.10 6 The support layer 30 further includes an impedance matching layer 40 having an acoustic impedance comprised within Pa·s / m. This acoustic impedance is adjusted to match the acoustic impedance of muscle and fat (1.3×10 6 Pa s / m~1.5×10 6 For example, the impedance matching layer 40 is silicone (acoustic impedance 1.6×10 6 It may be made of a bioplastic, such as brand Ecoflex® (acoustic impedance 1.053×10 6 It may be formed from a material having a viscosity of 100 Pa·s / m. The impedance matching layer 40 is disposed on the surface of the support layer 30 opposite to the surface in contact with the electrical connection layer 20. The impedance matching layer 40 typically has a thickness of 10 microns or more, for example, 50 microns to 5 mm. When the support layer 30 includes a film 35, the film is in contact with the impedance matching layer 40. The impedance matching layer 40 is intended to be in contact with the individual. In addition to effectively transmitting the pulse due to its impedance matching with the body tissue, this layer 40 also facilitates the holding of the sensor 100 on the individual, since its flexible and deformable material tends to "stick" to the contact surface by the adhesive friction of the clothes. Therefore, the presence of the impedance matching layer 40 in the second embodiment of the sensor 100 is particularly preferred when the measurement environment around the individual whose biosignal is to be captured is noisy.

[0026] In any of the described embodiments, it may be advantageous for the vibration sensor 100 to comprise a peripheral seal 60 surrounding at least the impedance matching layer 40 (if present), or surrounding all or part of the support layer 30 (if the impedance matching layer 40 is not present), as shown in Figures 3a and 3b, which allows the seal 60 to accommodate the local topology when the sensor 100 is placed in contact with an individual.

[0027] The support layer 30 of the vibration sensor 100 may also comprise a reinforcing structure 50, firmly connected to a peripheral zone of the support layer 30. The function of the reinforcing structure 50 is to immobilize the peripheral edges of the support layer 30 and the impedance matching layer 40 (if present), thus accentuating their deformations generated by the periodic pulsation of the biosignal to be measured. The reinforcing structure 50 can take various shapes, for example: a continuous frame (FIG. 4(a)), advantageously a ring (as shown in FIG. 2b), but optionally a rectangle, a triangle or another polygon, or - A discontinuous frame consisting of two rigid regions (Figure 4(b)), three rigid regions (Figure 4(c)) or more.

[0028] The reinforcing structure is advantageously made from a material having a hardness greater than 30 Shore D, such as PET (polyethylene terephthalate), PMMA (polymethyl methacrylate), PU (polyurethane), PVC (polyvinyl chloride), PP (polypropylene), etc. Considering the reduced overall thickness of the assembly comprising the laminate 10, the connecting layer 20, the support layer 30, and potentially the impedance matching layer 40, it may be advisable to provide a system that facilitates handling of the sensor 100 and promotes its robustness; the reinforcing structure 50 participates in such a system.

[0029] The device 200 according to the invention comprises, in addition to the vibration sensor 100 described above, an acoustic damping member 110 intended to be placed between the safety device 1 and the vibration sensor 100 . This member 110 is arranged above and spaced apart from the stack 10 of the vibration sensor 100 and is firmly connected to the support layer 30. It is arranged at a distance (along the z-axis in the figure) from the stack 10 (and thus without contact with it), typically at a distance of about 0.1 mm to 10 mm, so as not to hinder its deformation in relation to the support layer 30. The acoustic damping member 110 advantageously takes the form of a cover (Figures 6a(i), (ii)), the periphery of which is attached to the support layer 30 or, if present, to the reinforcing structure 50. By way of example, the thickness of the cover above the laminate 10 may vary between 0.1 mm and 20 mm. The acoustic damping member 110 is intended to insulate the acoustic sensor 100 (more specifically the support layer 30, which is deformed by vibrations, and the active layer 11, which is sensitive to said deformations) from ambient acoustic disturbances propagating through the air, i.e. engine sounds, road sounds, friction of air on the body, voices of passengers in the vehicle, radio, etc. It is preferably made of a flexible material of elastomer type, such as silicone, sorbothane or rubber. More generally, the flexible material of the acoustic damping member 110 can be qualified by its Shore hardness, having a hardness of 10 Shore OOO to 80 Shore OOO. In addition to its acoustic damping function, the member 110 is responsible for the robustness of the device 200, in particular by protecting the active layer 11 of the vibration sensor 100.

[0030] According to one variant, the acoustic damping member 110 may comprise several types of materials. When it is in the form of a cover, it is called a heterogeneous cover. The second material is selected to be of a rigidity of metallic or polymeric nature (for example aluminum, PVC). When the second material is a polymer, its hardness is preferably selected between 10 Shore D and 80 Shore D. The heterogeneous cover 110 is formed from an alternation of at least one first layer 110a of a flexible material and at least one second layer 110b made of a rigid material, as shown in Figure 6a(ii). The heterogeneous cover may also be composed of one or more porous materials, such as, for example, polyurethane foam.

[0031] Advantageously, the device 200 further comprises a mechanical damping member 120 whose role is to isolate the vibration sensor 100 from mechanical vibrations generated by the engine of the vehicle, by the road conditions and / or by the movements of the user and transmitted through the frame to the safety appliance 1. The mechanical damping member 120 is therefore intended to be in contact (directly or indirectly) with the safety appliance 1. This mechanical damping member 120 may be arranged on the acoustic damping member 110 or may be totally or partially integrated therein.

[0032] According to a first option, the mechanical damping member 120 consists of a body 120a forming a mass and at least one damper 120b (FIG. 6a(iii)). The body 120a is arranged relative to the acoustic damping member 110 and the damper is arranged at the side of the safety device 1.

[0033] The dampers 120b are defined by a stiffness k comprised between 0 (friction only) and 7 N / mm, and by a coefficient of friction f comprised between 0 (stiffness only) and 0.6. Each damper 120b may be formed, for example, by a metal spring, a resin, rubber or silicone post, or a simple mixed (rubber / metal) or hydraulic damper element. The body 120a has a mass m between 1 g and 1 kg. The mechanical damping member 120 forms a "mass-spring-piston" system that acts as a high-pass mechanical filter. By adjusting the mass m, the stiffness k and the friction coefficient f, it is possible to vary the properties of the mechanical filter, in particular to damp the mechanical vibrations transmitted to the safety device 1. It should be noted that the mass of the acoustic damping member 110 and the mass of the vibration sensor 100 must be taken into account and added to the mass of the body 120a to reach the desired mechanical filter characteristics. The mechanical filter is targeted to cross / attenuate parasitic frequencies located in the region of interest. So in the ideal case, to cut off all stray frequencies arising from the chassis (mechanical vibrations), the cutoff frequency of the filter should be

[0034]

number

[0035] is preferably about 150Hz, and its attenuation rate is

[0036]

number

[0037] It is desirable to have r as close to 1 as possible to have the best possible attenuation. In practice, of course, a compromise is made between this ideal case and the design constraints of the device 200.

[0038] According to a second option, the mechanical damping member 120 is partially integrated in the acoustic damping member 110, i.e. the body 120a consists of a layer of rigid material 110b (for example in the form of a heterogeneous cover as shown in Fig. 6a) which constitutes said acoustic damping member 110. The damping part 120b of the mechanical damping member 120 is then attached to the acoustic damping member 110 and may be formed by the different elements described in the first option.

[0039] According to a third option, the mechanical damping member 120 is fully integrated in the acoustic damping member 110. To this end, the mechanical damping member 120 (contained in the acoustic damping member 110) may be made from a composite material having viscoelastic properties.

[0040] The device 200 according to the invention may have a generally circular, square, rectangular or polygonal shape in the main plane (x, y). As shown in Fig. 6b, it is intended to be placed between the safety device 1 and the individual seated in the vehicle. The face of the device 200, which is located on the side of the support layer 30 of the vibration sensor 100 (and on the side of the impedance matching layer 40, if present), is placed against the individual's chest, preferably in the area where the heart rate or the respiratory rate is palpable. The other face of the device 200, which is located on the side of the acoustic damping member 110 (and the mechanical damping member 120, if present), is held against the safety device 1. The contact between the device 200 and the device 1 is preferably performed by a slide fastener 201 (Fig. 6b), in particular the face of the device 200 is rigidly connected (adhesively bonded or mechanically attached) to the support element 201a of the coupler 201, which element is attached to the safety device 1 by a slide clip 201b.

[0041] The device 200 according to the invention has the advantage that it significantly attenuates frequencies outside the range of frequencies to be measured (typically the range of frequencies between 0.2 Hz and 500 Hz for heart rate and respiratory rhythm, or frequencies below 70 Hz) and also attenuates parasitic frequencies located within the frequency range of interest. In particular, it has been observed that speech and other ambient sounds do not contaminate the measurement signal. Thus, the acoustic environment of the individual when the measurement is performed does not have to be quiet and soundless. This is possible due to the particular structure of the vibration sensor 100 and due to the presence of the sound-damping member 110. In addition, the presence of the mechanical damping member 120 (or of at least one mechanical energy absorber 210, as will be explained below with reference to the safety system that is the subject of the present invention) significantly dampens the mechanical vibrations generated by the motor during operation, and optionally road irregularities, vibrations transmitted via the vehicle chassis to the safety implement 1. Neutralizing these parasitic mechanical vibrations allows reliable and reproducible capture of an individual's biosignals by the vibration sensor 100.

[0042] Advantageously, the device 200 is associated with a fabric 130 and a foam 140 to improve the comfort of the user (FIG. 6b). The fabric 130 may for example border the support layer 30 and the impedance matching layer 40, if present, which generally borders all or part of the vibration sensor 100 and thus can provide a smooth and uniform contact surface with the individual, which allows to accommodate variations in user morphology, clothing type and / or adjustment of the safety equipment 1. The foam 140 typically forms a link between the fabric 130 and the fastener 201, which is flexible and deformable and does not or only very little alters the mechanical filter defined by the mechanical damping member 120. The fabric 130 may be formed from cotton, nylon, or polyethylene, and the foam 140 may be formed from polyurethane, polyethylene, or polystyrene.

[0043] The device 200 associated with a safety device 1 in a vehicle allows the measurement of at least one raw signal representative of a periodic biosignal of an individual seated in the vehicle. The device 200 further comprises an electronic terminal 150 electrically connected to the vibration sensor 100, in order to analyse and interpret the raw signal and then extract the periodic bio-signal or information about this bio-signal. It should be noted that the device 200 may comprise a vibration sensor 100 (Fig. 5(a), (b)) or a plurality (two or more) sensors 100 (Fig. 5(c)) connected to the electronic terminal 150. When there are several sensors 100, they may measure the same signal or different bio-signals (heart rate and respiration) of an individual.

[0044] For connecting the vibration sensor 100 to the electronic terminal 150, the printed circuit 31 of the vibration sensor 100 may comprise a wire connection element 31b, for example a strip in the form of a web as shown in Figures 2a, 2b, 3a, 3b and 5(a). End pieces of the wire connection element 31b are provided with electrical contact connectors connected to electrical terminals 32, 33 of the printed circuit 31, which may be connected to the electronic terminal 150. The electronic terminal 150 can be attached to the sensor 100 or can be located remote from the sensor 100, in particular on a mounting module for mounting to another part of the safety appliance 1 or the vehicle. The electronic terminal 150 can be connected to or integrated into a more complex external system, such as a fixed or optionally mobile monitor. Alternatively, the electronic terminal 150 can be arranged on the acoustic damping member 110 and can form all or part of the body 120a of the mechanical damping member 120. This configuration ensures a very compact device 200. In this case, it is possible to envisage a wire connection element 31b for electrically connecting the vibration sensor 100 and the terminal 150, while contact plugs 82, 83 rise vertically from the printed circuit 31 of the sensor 100 to the surface of the acoustic damping member 110, for example via a reinforcing structure 50 (Figure 5(b)).

[0045] The terminal 150 may include various electronic stages that allow to analyze and interpret the raw signal measured by the vibration sensor 100. The analog stage for conditioning the raw signal measured by the vibration sensor 100 first amplifies and filters the electrical signal received from the sensor 100. This stage typically consists of a first block of charge amplification type, whose resistance ratio sets the amplification gain of the electrical signal received from the sensor 100, and a second block of Sallen & Key filter type, which allows to filter the frequencies beyond the acoustic spectrum of the target biosignal. The electronic terminal 150 then includes a stage of analog-to-digital conversion of the signal coming from the conditioning stage. A digital signal processing stage, then consisting of a microcontroller, performs the shaping of the signal by calculating the Shannon energy envelope function. Finally, from the shaped signal, the desired output parameters representative of said biosignal may be calculated.

[0046] The collected data relating to the biosignal or output parameter of interest can be interpreted in real time and trigger a response of a secondary system included in or external to the device 200. The response can be, for example, information feedback (visual, audible, mechanical, vibratory, etc.) and / or the triggering of one or more of the following actions: -Mechanical(s): opening / closing the system. -Electrical(s): On / Off / Change systems, hydraulic, pneumatic, heat etc. In all cases, the secondary system's response is intended to inform or warn an individual (typically the driver of the vehicle) if detected vital signs indicate a risk of drowsiness or other abnormal condition.

[0047] To allow the transmission of the desired output parameters to a possible external system, the electronic terminal 150 may include a communication stage: for example, well-known connection protocols (CAN (Controller Area Network), UART (Universal Asynchronous Receiver / Transmitter), USB (Universal Serial Bus)) or wireless data transmission (Wi-Fi, Bluetooth, etc.) may be used. To make the device 200 autonomous, it is also possible to provide a battery, preferably rechargeable, that allows the different stages of said vibration sensor 100 and / or electronic terminal 150 to be supplied with energy. When the terminal 150 is away from the area of ​​the vehicle's dashboard, it can be powered by the vehicle's battery.

[0048] As mentioned above, the device 200 can be decomposed into various configurations: a portable autonomous device that can be placed on any vehicle safety appliance 1; A fixed installation, in which the terminal 150 is connected to the sensor 100 by wires or is integrated into a fixed, more complex external system (mounted on or integrated into the dashboard of the vehicle).

[0049] The invention also relates to a safety system for a vehicle comprising a safety appliance 1 rigidly connected (directly or indirectly) to the chassis of the vehicle at at least one contact point 2 (FIG. 1). The safety appliance 1 can be directly connected to the chassis, typically via at least three contact points 2, e.g. for a seat belt. Alternatively, the safety appliance 1 can be indirectly connected to the chassis, in which case the safety appliance 1 is rigidly connected to the vehicle seat, which in turn is rigidly connected to the chassis at one or more contact points 2.

[0050] The safety system comprises the aforementioned device 200 for measuring at least one periodic biosignal of an individual (eg the driver of a vehicle), attached to a safety device 1 by means of a slide fastener 201 . When equipped with a mechanical damping member 120, the device 200 isolates the vibration sensor 100 from the engine's mechanical vibrations transmitted by the chassis to the safety equipment 1, as shown in the application example below, thereby enabling the collection and efficient analysis of personal biosignals within the vehicle during operation.

[0051] The device 200 according to the invention can also be implemented in a safety system without the mechanical damping member 120. In this case, the safety system comprises at least one mechanical energy absorber 210 arranged at at least one contact point 2 so as to isolate the safety device 1 from chassis vibrations upstream of the vibration sensor 100. If the safety device 1 is connected to the chassis at three (or optionally four) contact points 2, it is advantageous to place the mechanical energy absorber 210 at at least one contact point 2, or indeed at each of the contact points 2. If the safety device 1 is connected to the seat, the mechanical energy absorber 210 is preferentially placed at the contact point 2(s) between the seat and the vehicle chassis.

[0052] Of course, when the safety device 1 is directly connected to the chassis, it is also possible to arrange the mechanical energy absorber 2 at the contact point(s) 2 between the seat and the chassis. The mechanical energy absorber 210 forms a mechanical filter and therefore comprises a body (mass) and a damper (stiffness, coefficient of friction) as described with reference to the mechanical damping member 120 .

[0053] Finally, it is conceivable to implement both the device 200 with a mechanical damping member 120 and a mechanical energy absorber 210 offset over all or part of the direct or indirect contact points 2 between the safety device 1 and the chassis. Such a configuration further allows improving the quality of the raw signal measured by the vibration sensor 100 by significantly limiting the parasitic noise and vibrations associated with the operation of the engine and the movement of the vehicle.

[0054] Representative embodiments: Next, a description will be given of an embodiment of the manufacture of the vibration sensor 100 and the device 200. Of course, this embodiment is not limiting, since there are other methods of stacking and assembling different types of layers that can be implemented to manufacture the device 200 according to the invention. To manufacture the laminate 10 of the vibration sensor 100, it is possible to use a transfer method, in particular similar to that described by T Dufay et al. in the publication "Flexible PZT thin film transferred on polymer substrate" (Surface and Coatings Technology, Elsevier, 2018, 343, pp. 148-152). A solution of PZT (lead zirconate titanate) precursor is deposited by spin coating onto a sacrificial substrate (e.g. aluminum) to form a viscous layer. Openings are formed through said layer to allow the passage of electrical paths. A heat treatment of 650°C is then applied to crystallize the PZT and form an active layer 11 made of piezoelectric material with a thickness of 5 microns. A platinum contact electrode 12 with a thickness of 400 nm is deposited by a chemical vapor deposition technique (e.g. PECVD (Plasma Enhanced Chemical Vapor Deposition)) on the upper (free) surface of the active layer 11 made of PZT and then covered with a polyurethane adhesive layer. Openings are also made through the electrode / adhesive layer stack to allow electrical paths to pass. To facilitate handling of the active layer 11, a temporary layer made of a polymer (e.g. PET) with a thickness of 200 microns is attached to the thermocompressed polyurethane adhesive layer. The temporary layer is opened to allow the passage of electrical paths and filled with a conductive adhesive, which forms a conductive via 14 in electrical contact with the contact electrode 12. The sacrificial substrate is then chemically etched until the underside of the active layer 11 made of PZT is exposed. The other contact electrodes 13 and the studs 12a in electrical contact with the vias 14 are formed by aluminum deposition (about 400 nm) on the underside of the PZT.

[0055] The manufacturing method may allow the creation of a PZT film with large lateral dimensions, which is then cut to define an active layer 11 with lateral dimensions desired for its integration into a vibration sensor 100 according to the invention. In the example described, the active layer 11 has lateral dimensions (along the main planes (x, y)) of 5 mm by 15 mm.

[0056] A printed circuit board (PCB) 31 is then selected, having a thickness of 100 microns, lateral dimensions substantially identical to those of the active layer 11, and comprising two electrical terminals 32, 33. An anisotropic conductive film (ACF) 20 is laminated onto the printed circuit 31. Using a handling machine (of the "pick and place" type), the active layer 11 is placed against the connection layer 20, such that the respective electrodes 12a, 13 (on the lower surface of the active layer 11) are aligned with the electrical terminals 32, 33 of the printed circuit 31, and then assembly by thermocompression is performed. The temporary polymer layer may then be removed. The printed circuit 31 is then bonded to a PVC membrane 35, 300 microns thick and 50 mm lateral dimension (or diameter), completing the formation of the support layer 30. An impedance matching layer 40 made of silicone, 3 mm thick, can be assembled by lamination, screen printing or moulding to the membrane 35. A polypropylene reinforcing structure 50 and a silicone peripheral seal 60 are attached to the periphery of the membrane 35 by fitting. Above and at a distance from the active layer 11, a silicone cover forming an acoustic damping member 110 is moulded onto and then glued onto the reinforcing structure 50. It has a thickness of 2 mm. The mechanical damping member 120 may also be formed, consisting of a rubber post 120b joined to a steel body 120a of thickness 5 mm. The body 120a is glued to the acoustic damping member 110. The post 120b is glued on the side of its free end to a support element 201a of a fastener 201 which may be associated with a safety device 1 of the vehicle (in this example a seat belt 1). The fastener 201 may for example be formed from polyoxymethylene. For user comfort, the assembly may be covered with fabric 130 and / or foam 140 around the periphery of the measurement area.

[0057] In this embodiment, the printed circuit 31 comprises wire elements 31b (webs) making it possible to connect, via electrical contact plugs, the electrical terminals 32, 33 of the printed circuit 31 to an electronic terminal 150. The terminal 150 comprises the electronic stage described in the general description. It is placed, for example, under the seat of the user.

[0058] An example application of the thus formed device 200 for measuring the heart rate of a driver is shown in Figures 7a and 7b. To measure the heart rate, the device 200 is adjusted in height along the seat belt 1 and placed substantially on the left side of the individual's chest, the impedance matching layer 40 of the vibration sensor 100 is placed in contact with the individual's clothing, and the mechanical damping member 120 is in contact with the seat belt 1 via a sliding clip 201.

[0059] 7a shows two raw spectrograms A, B acquired by the vibration sensor 100 as described above on a frequency scale ranging from 0 to 150 Hz (acquisition frequency 128 kHz). In the case of spectrogram A, the measurement device does not comprise an acoustic damping member 110 or a mechanical damping member 120, and the safety system also does not comprise a mechanical energy absorber 210. In the case of spectrogram B, the device 200 according to the embodiment described above comprises an acoustic damping member 110 and a mechanical damping member 120. When the vehicle is stationary, both spectrograms A, B show regular peaks which, after processing, provide reliable information on the driver's heart rate, this information being reliable regardless of the ambient sound level inside the vehicle. Conversely, as soon as the vehicle is in motion, the engine vibrations generate enormous parasitic noises and vibrations that render spectrogram A unusable. The device 200 according to the invention allows to obtain a much less noisy spectrogram B, due to the presence of the acoustic damping member 110 and the mechanical damping member 120. It should be noted that similar results are obtained with the device 200 without the mechanical damping member 120, if the vehicle safety system comprises at least one mechanical energy absorber 210 at the direct or indirect contact point(s) 2 between the seat belt 1 and the chassis.

[0060] Figure 7b shows an extract B' of about 15 seconds of spectrogram B during a period when the vehicle is in motion: the regular peaks representing the driver's heart rate are now more clearly distinguished. Spectrogram B'' is obtained by applying a filter between 40 Hz and 70 Hz and normalizing the signal. The peaks shown on spectrogram B'' can be visualized in a waveform. This is signal B''' and reveals peaks representative of the driver's heart rate. From signal B''' it is therefore possible to extract, with an excellent level of accuracy, periodic signals and / or output parameters representative of the individual's heart rate. It is therefore possible to reliably detect changes in heart rate (or similarly breathing rate) that are likely to signal that the driver is falling asleep or some other dangerous situation, in which case the device 200 can trigger an action (e.g., a sound or light signal) as previously described. As previously mentioned, in general, the non-intrusive device 200 for measuring periodic vital signs according to the present invention provides reliable information regarding the driver's vital signs regardless of the acoustic environment inside the vehicle, whether stationary or in motion.

[0061] Naturally, the invention is not limited to the embodiments and examples described, but variants can be provided thereto without departing from the scope of the invention as defined by the claims.

Claims

1. A device (200) for measuring at least one periodic biosignal from an individual, intended to be attached to a vehicle safety device (1) so as to be placed between said device and said device (1), said device (200) comprising: a vibration sensor (100), * A stack (10) extending parallel to a main plane (x, y) and including an active layer (11) made of a piezoelectric material and two contact electrodes (12, 13) arranged on at least one face of said active layer (11); * a flexible support layer (30) configured to transmit deformations to the active layer (11) of the laminate (10) with each pulse of the biosignal, the support layer (30) comprising a printed circuit (31) extending parallel to the main planes (x, y) and provided with two electrical terminals (32, 33), the support layer (30) being intended to be placed against the individual; * an electrical connection layer (20) disposed between the laminate (10) and the support layer (30) and connecting each of the contact electrodes (12, 13) to an electrical terminal (32, 33); A vibration sensor (100) comprising: - An apparatus (200) comprising an acoustic damping member (110) intended to be placed between the safety device (1) and the vibration sensor (100), the acoustic damping member (110) being firmly connected to the support layer (30) and positioned above the stack (10) and at a distance from the stack (10).

2. 2. The apparatus (200) of claim 1, wherein the acoustic damping member comprises a cover made of a flexible material having a hardness of 10 Shore OO to 80 Shore OO and rigidly connected by its periphery to the support layer (30).

3. The apparatus (200) of claim 2, wherein the cover is non-homogeneous and comprises a second rigid material selected from a metal or a polymer having a hardness between 10 Shore D and 80 Shore D.

4. 2. The device (200) according to claim 1, comprising a mechanical damping member (120) integrated in whole or in part on or within the acoustic damping member (110), the mechanical damping member (120) being intended to be in direct or indirect contact with the safety device (1).

5. The apparatus (200) of claim 4, wherein the mechanical damping member (120) comprises at least one damper and optionally a body forming a mass.

6. The device (200) of claim 1, wherein the active layer (11) of the stack (10) has a thickness of less than or equal to 20 microns and a Young's modulus of more than or equal to 60 GPa.

7. 5.10 5 Pa・s / m~3.10 6 2. The device (200) of claim 1, further comprising an impedance matching layer (40) having an acoustic impedance comprised in Pa·s / m and arranged on a surface of the support layer (30) opposite to the surface in contact with the electrical connection layer (20).

8. - said contact electrodes (12, 12a, 13) have a cumulative thickness less than twice the thickness of said active layer (11); - said support layer (30) is self-supporting and has a thickness of less than or equal to 500 microns; The device (200) of claim 7, wherein the impedance matching layer (40) has a thickness of 10 microns or more.

9. 2. The device (200) of claim 1, wherein the support layer (30) comprises a membrane (35) disposed on a side of the printed circuit (31) opposite to the side in contact with the electrical connection layer (20).

10. 2. The apparatus (200) of claim 1, wherein the support layer (30) comprises a reinforcing structure (50) rigidly connected to a peripheral zone of the support layer (30), and the acoustic damping member (110) is rigidly connected to the reinforcing structure (50).

11. An electronic terminal (150) connected to said vibration sensor (100) for analyzing and interpreting the raw signal and for extracting said periodic biosignal or an output parameter representative of said periodic biosignal.

12. The electronic terminal (150), - an analog stage for conditioning the raw signal measured by the vibration sensor (100); an analog-to-digital conversion stage for the signal coming from said analog stage; - a digital signal processing stage for forming a digital signal and for calculating output parameters representative of said bio-signal.

13. A vehicle safety system, comprising: a safety device (1) associated with the seat and rigidly connected to the chassis of said vehicle at at least one direct or indirect contact point (2); - a device (200) for measuring at least one periodic vital sign from an individual according to one of claims 1 to 12, attached to said safety device (1) by means of a slide fastener (201), - at least one mechanical energy absorber (210) arranged at at least one contact point (2) so as to isolate said safety device (1) from mechanical vibrations of the chassis.

14. 14. A safety system for a vehicle according to claim 13, wherein the safety device (1) is directly connected to the chassis by at least three contact points (2) and a mechanical energy absorber (210) is integrated into at least one of the contact points (2).

15. 14. A safety system for a vehicle according to claim 13, wherein the safety device (1) is connected to the seat, the seat being rigidly connected to the chassis by at least one contact point (2), and a mechanical energy absorber (210) is integrated into the contact point (2).

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